The application of biotechnology to plants has yielded many agricultural gains. For example, biotechnology has been used to improve various properties of plants such as resistance to pests and diseases, resistance to herbicides, and the improvement of various seed and fruit traits. Many further applications of plant biotechnology are anticipated and these include the modification of specific traits that may be of agronomic interest or of interest in the processing and use of plant-derived products. In many instances, this could be undertaken by the manipulation of endogenous genes which encode these traits, however, the sophisticated means to achieve up- and down-regulation of such endogenous genes is, in many cases, not yet available. In addition, plants also hold great promise as biological “factories” for a variety of chemical products including enzymes and compounds for industrial and pharmaceutical use. However, it is expected that the continuous production of high concentrations of gene products and compounds for such use may have deleterious consequences for the host plant and consequently, more sophisticated mechanisms for expressing such genes are required.
Accordingly, gene switches are currently of interest for the control of timing and/or dosage of gene expression in plants. In particular, the development of gene switches that can be directed towards any gene in a plant chromosome is highly desirable.